Method of preparing intaglio printing plates



Feb. 27, 1951 WHELDON 2,543,393

METHOD OF PREPARING INTAGLIO PRINTING PLATES Filed Dec. 31, 1948 INVENTOR. Qw 76/500095 M95100 BY \S i Q WWX ORlG.

Patented Feb. 27, 1951 Mn'rnoD or Plasma-Inc rN'rAGLio ram'r uo PLATES Theodore WheldonQV/est Englewood, N. J., as-

signorto Publication Eorporation, New York, N. Y., a corporation of New York Application n gate 31, 1948, Serial No. 68,718

The present invention relates to methods of forming intaglio printing surfaces and embodies, more specifically, an improvement'method by means of which certain photographic operations are utilized to prepare a resist which is then used in a conventional way to etch the desired printing surface. 1

More specifically, the invention has for an object the provision of-certain improved photographic steps by means of which the subject to be reproduced is incorporated in a sensitized gelatin insuch fashion that portions of the sensitized gelatin are insolubilized by the use of light and in the form of dots of varying size and thicknesses in proportion to the varying tones of the original subject matter.

The foregoing is accomplished by the utilization of a screen positive image of the subject matter to be reproduced, such screen positive being exposed to the sensitized gelatin twice, once in contact, and once suitably spaced from the sensitized gelatin.

In order that the invention will be readil understood, it will be described in connection with the accompanying drawing, wherein the single figure is a diagrammatic illustration of the various steps of the method of the present invention.

Referring to the drawing, the original subject is illustrated at I as having a high-light region la, a middle tone region lb, and a shadow tone region Ic. From this original subject, a negative transparency 2 is formed in the usual way. This negative transparency will show the tones of the original in reverse relationship, that is, the highlight area la will be of relatively great density while the shadow tone area to will be of relatively light tone.

The next operation is also a conventional operation forming a screen positive from the negative 2. This operation is illustrated diagrammatically within the block 3 wherein negative 2 is exposed by a suitable light source 3a (such as an evenly illuminated ground glass) through a lens system to and a suitable screen 30 on to a photographic emulsion 3d. The screen 30 may be a half-tone screen of conventional type, the characteristic of which is that the image is broken up into a series of minute dots corresponding in position to the apertures in the screen. These dots vary in size in accordance with the intensity of light passing through the screen apertures. For example, where the negative is relatively dark (corresponding to the high-light area i a) small dots are formed as illustrated at 3d Where 3 Claims. (01. 95-5.6)

2 the negative is relatively transparent (corresponding to the shadow tone area to) large dots 3d are formed, and where intermediate tones exist, intermediate dots M are formed. In the areas not occupied by the dots above mentioned, the screen positive is transparent.

The size of the dots of the screen positive are also controlled by the spacing of the screen from the photographic emulsion (screen distance), and by the intensity of the light passing through the screen (determined by the duration and also the actual light intensity of the light source). This is generally known and need not be explained in detail herein. It is sufficient to state that, by controlling the screen distance and exposure, the size of the dots on the screen positive may be controlled so that none of the dots touch or overlap to an extent that would produce connected pockets in the printing plate. In other Words, a screen positive with the character described in the patent to Wilkinson No. 2,155,458 may be formed.

Having made the screen positive 3d, the photographic operations essential to the present invention are then followed. These operations center about the exposure of the screen positive upon the sensitized gelatin (commonly called carbon tissue) which is later to be used as the resist in the operation of etching the image in the printing surface. Upon this sensitized gelatin two exposures are made through the screen positive 3d. Although the order of these exposures is immaterial, in the diagrammatic illustration of the drawing the first exposure is that of ex posing the sensitized gelatin to a source of light through the screen positive 3d. The sensitized gelatin is illustrated at 3a in the block 4 in the drawing, being illustrated as having a paper backing ib. Where the screen positive is transparent, the underlying portions to of the sensitized gelatin are fully exposed, as illustrated by hatching. Beneath the respective dots 301 3d and 311 unexposed areas 165 4:2 and 4:5 respectively, remain. Any suitable light source ie may be used in accordance with common practice.

After completing the first exposure, the sensitized gelatin 3a is again exposed through the screen positive 3d behind a diffused source of light. This light source is represented diagrammatically by a dififuser 4 The screen positive 3d is spaced from the sensitized gelatin 4a by means of a transparent plate or film 4g, and the sheet of the difiused light and the spacing of the screen positive from the sensitized gelatin is such that the screen formation of the screen positive is lost upon the sensitized gelatin, and the latter thus, in effect, sees only the variation of the tone of the original subject as translated by the varying sized dots in relation to the transparent area in which those dots occur. Thus, where the dots are small, a relatively intense light appears under that area on the sensitized gelatin, and the unexposed areas 401 are exposed substantially as indicated by the hatching at Mi l. In the middle tone areas where the dots 3d are larger, the previously unexposed areas 4d are exposed to a depth indicated by the hatching M 1. In the shadow tone areas where the dots 3d are relatively large, the effect of the exposure is least, and the previously unexposed areas id are exposed to a depth illustrated by the hatching at 4:2 1.

After the two exposures illustrated diagrammatically in the block 4 have been completed, the carbon tissue is used in a conventional manner to form an intaglio printing surface. For example, as indicated in block 5 in the drawing, it is applied to a copper surface 5a which is to be the printing surface, the paper backing is stripped, and the unexposed portions of the sensitized galatin (which portions are soluble in warm water) are dissolved away. A suitable etching medium is then used, and pockets are thus etched in the printing surface 5a that correspond in area to the size of the dots, and in depth to the intensity of the light by which those dots were formed. These pockets are illustrated at 511 511 and M The printing plate is illustrated in cross-sectional form in the block 6 of the diagrammatic showing of the drawing.

While the invention has been described with specific reference to the structure shown in the accompanying drawing, it is not to be limited save as defined in the appended claims.

I claim:

1. The method of forming an intaglio printing surface comprising forming a screen positive of subject matter to be reproduced, twice exposing in any order the screen positive upon a layer of light-sensitive gelatin, onc in contact therewith and once spaced therefrom to diffuse the screen pattern, developing the light-sensitive gelatin to form a resist and etching a surface through the gelatin resist to produce an intaglio printing surface.

2. The method of forming an intaglio printing surface comprising forming a screen positive of subject matter to be reproduced, twice exposing in any order the screen positive upon a layer of light-sensitive gelatin, once in contact therewith and once spaced therefrom to diffuse the screen pattern, using a diffused source of light to lose the effect of the screen formation upon the sensitized gelatin, developing the gelatin to form a resist and etching a surface through the gelatin resist to produce an intaglio printing surface.

3. The method of forming an intaglio printing surface comprising forming a screen positive of subject matter to be reproduced, exposing the screen positive in a contact photographic rinting operation upon a layer of bichromated gelatin, spacing the screen positive from the resist and exposing from a diffused source of light to lose the effect of the screen formation upon the sensitized gelatin, developing the gelatin to form a resist and etching a surface through the gelatin resist to produce an intaglio printing surface.

THEODORE WHELDON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 0 Number Name Date 1,532,696 Hassard Apr. '7, 1925 2,096,794 Dultgen Oct. 26, 1937 

1. THE METHOD OF FORMING AN INTAGLIO PRINTING SURFACE COMPRISING FORMING A SCREEN POSITIVE OF SUBJECT MATTER TO BE REPRODUCED, TWICE EXPOSING IN ANY ORDER THE SCREEN POSITIVE UPON A LAYER OF LIGHT-SENSITIVE GALATIN, ONCE IN CONTACT THEREWITH AND ONCE SPACED THEREFROM TO DIFFUSE THE SCREEN PATTERN, DEVELOPING THE LIGHT-SENSITIVE GELATIN TO FORM A RESIST AND ETCHING A SURFACE THROUGH THE GELATIN RESIST TO PRODUCE AN INTAGLIO PRINTING SURFACE. 